Natural fluctuation or decline problem?
From: Decline in amphibian populations - Background problem
Ambystoma macrodactylum croceum Santa Cruz Long-toed Salamander, Long-toed Salamander Santa Cruz) is a subspecies of salamander severely threatened Assume that the interference of humans or pets is one of the causes of its decline.
From the 1950s to the late 1980s, some researchers have noticed a decline in amphibian populations. This decline was to have been a leading indicator of the degradation of natural environments. The scientific community was skeptical about this test and the importance of this decline Indeed, some zoologists advanced than the population of most organisms, including amphibians, known natural variations. Lack of information on changes in populations over a longer term did not determine whether the observations were sufficient to conclude. Without consensus, we therefore expect to have sufficient information to mobilize resources for a program of conservation.
To do this, we improved the system of population monitoring, affecting an increasing number of students in projects of direct observations of the mortality of amphibians to determine the number and causes of mortality. Finally, in the late 1990s, the scientific community recognized the overall decline of amphibian populations worldwide and the threat it poses to biodiversity
Indeed, amphibians play an important role in maintaining balanced ecosystems. They are now the prey, sometimes predators of many other species. The eggs and tadpoles are a rich source of food for birds and fish. In turn, amphibians consume vast quantities of insects, and sometimes even rodents. They can form a significant portion of the vertebrate biomass in some areas, exceeding the combined biomass of birds and mammals. Despite their small size, amphibians play an important role in ecosystems. When a species of frog disappears, this can cause the disappearance of cascading several other species, starting with the species commensal such as the mule of Necturus, which larval development depends on the presence of his host, the Mudpuppy
Potential causes of decline
Based on research by James P. Collins and Andrew T. Storfer, two sets of assumptions about the decline were piled
The first includes general factors concerning the crisis of global biodiversity: destruction, modification and fragmentation of natural habitats, introduction of invasive species and overfishing. The study of these threats enables better understanding of amphibian declines in aspects related to global ecological processes. However, the decline also affects populations of amphibians in remote environments without apparent disturbance.
The second appeals to factors more complex and elusive and is likely formed by climate change, increased UV-B radiation, the discharge of chemical pollutants in the environment, new emerging infectious diseases, and deformities or malformations of organisms. The mechanisms underlying these factors are complex and can add up the initial factors, and habitat destruction and introduction of alien species introduced exacerbates the phenomenon of decline.
There is no one single cause to the decline of amphibians. All the aforementioned factors threaten these people with degrees or lower. Most causes of this decline are finally understood and explained. Beyond amphibians, other groups of organisms suffer from the same disturbance.
Destruction and fragmentation of natural habitats
The salamanders are protected from predators by a toxic mucus and color blind ... that they are useless against vehicles.
The modification or destruction of natural habitats is the factor that, globally, affecting most populations of amphibians. Because amphibians generally need both terrestrial and aquatic habitats to survive a threat to one of the two habitats may have serious consequences for their populations. Amphibians are more vulnerable to changes in natural environments that organisms requiring only a single habitat type
The habitat fragmentation occurs when natural areas suitable for different life amphibians are isolated from each other by changes in physical character, such as when a forested area is surrounded on all sides by areas of agricultural crops. Small populations persist in these fragments often face a persistent risk of inbreeding, the genetic drift or of extinction due to small fluctuations of the environment.
In most European countries, the loss of wetlands is on very important areas. Thus in Switzerland these areas decreased by almost 90% for 150 years or even 100% in some areas From 1953 to 1959, nearly 66% of breeding habitats of the Alpine newt, the newt, the yellow-bellied toad, the common toad, the green tree frog, the frog and the frog have been destroyed in the upper valley of the Rhine as a result of beach replenishment and road construction
Since the 1950s, many amphibians in the Mediterranean region are becoming very rare due to the destruction of their habitat
The destruction of wetlands is the main cause of depletion of the frog (over 99% of extinction in some areas) and common toad in the 1950s and 1960s in Great Britain
Some species do not live on their specific areas of reproduction must migrate to reach the wetlands. Reproductive individuals exposed then to go to and return to areas where their safety is not ensured. This is the case for road crossings. When spawning is no longer available, a wall can sometimes be enough to make people disappear.
The vocalizations are essential for the reproduction of many amphibians. An increase in noise caused by human activities may also be the cause of reduced fertility that ultimately cause a decline. A study in Thailand showed that, subject to the noises of human activities, calls for amphibian species declined and increased for others. The relationship between noise and decline has not been shown